A laminated glass is a safety glass because few glass fragments are scattered even when fractured by an external impact. Laminated glass is widely employed as window glass in aircraft, buildings, vehicles such as automobiles, and so forth. An example of laminated glass is laminated glass in which an interlayer film for laminated glass, comprising a plasticizer and a polyvinyl butyral resin, is interposed between at least a pair of glass sheets.
The infrared wavelength region, which occurs at longer wavelengths than the visible light region, occupies the wavelength region that is 780 nm or more. The amount of energy from infrared radiation is about 10% of an amount of energy from ultraviolet radiation. However, infrared radiation, because it is released as heat when absorbed by a material, does have the ability to raise the ambient temperature. For example, the temperature rise in the interior of an automobile can be restrained when the infrared radiation penetrating the windshield and side windows of the automobile is blocked. In recent years there has been a need to lower the infrared transmittance of laminated glass due to the trend of increasing open areas in, for example, automobiles and the like.
Patent Document 1 discloses an interlayer film for laminated glass; this interlayer film contains a polyvinyl acetal resin and heat shielding fine particles, for example, tin-doped indium oxide fine particles, antimony-doped tin oxide fine particles, and so forth. Laminated glass that employs an interlayer film in which heat shielding fine particles is dispersed exhibits an excellent heat shielding performance. However, a problem here has been the high cost of tin-doped indium oxide fine particles and antimony-doped tin oxide fine particles. This has led to efforts to use zinc oxide fine particles as heat shielding fine particles.
Patent Document 2 discloses a zinc oxide fine particle in which the metal components are zinc and at least one metal element selected from Group IIIB metal elements and Group IVB metal elements. This zinc oxide fine particle has a zinc content of 80 to 99.9% expressed as the ratio of the number of zinc atoms to the total number of the aforementioned metal component atoms and exhibits zinc oxide crystallinity according to x-ray diffraction. This zinc oxide fine particle is described as having an excellent shielding effect for infrared radiation.
However, the laminated glass has tended to exhibit a high haze in the case of an interlayer film for laminated glass produced by incorporating the zinc oxide fine particle disclosed in Patent Document 2 in a thermoplastic resin, e.g., polyvinyl acetal resin and so forth. The following methods can be contemplated for reducing this laminated glass haze: lowering the zinc oxide fine particle content; thoroughly dispersing the zinc oxide fine particles by applying high shear force to the zinc oxide fine particles.
However, the interlayer films for laminated glass obtained using these methods have suffered from the problem of a high infrared transmittance.
Patent Document No. 1: WO 01/25162
Patent Document No. 2: Japanese Kokai Publication 2003-54947 (JP-A 2003-54947)